In order to design a fluorescent probe with a long wavelength and multiple hydrogen bond sites for thymine, 3-(4-chloro-6-methylamino-1,3,5-triazinylamino)-7dimethylamino-2-methylphenazine is synthesized by subsequently reacting neutral red and methylamine with cyanuric chloride. Its recognition behavior for thymine and its spectroscopic properties in different solvents are studied. The probe's fluorescence can be selectively quenched by thymine instead of guanine, indicating that fully complementary hydrogen bonding plays a key role in such recognition processes. In addition, the recognition mechanism of the probe for thymine and the bathochromic shift of its fluorescence spectra with the solvent polarity are also discussed. (C) 2003 Wiley Periodicals, Inc.